A thermal printhead is a device used for printing images or letters by locally raising the temperature of a recording medium such as thermal paper (see e.g. Patent Document 1): FIG. 3 shows an example of conventional thermal printhead. The thermal printhead X shown in the figure includes a substrate 91, on which a partial glaze 92 is formed. An electrode pattern 93 is formed on the substrate 91. A heating resistor 94 connected to the electrode pattern 93 and extending in the primary scanning direction is also formed on the substrate 91. The heating resistor 94 is covered with a protective film 95. In printing, a sheet of thermal paper is moved relative to the protective film 95 in the secondary scanning direction while being pressed against the protective film.
The thermal printhead X has a drawback that thermal paper may stick to the protective film 95 during the printing operation. Generally, the surface of the thermal paper sheet is coated with resin. The resin coating melts due to the heat from the thermal printhead X and adheres to the protective film 95. When the resin coating solidifies in this state, thermal paper sticks to the protective film 95.
The likelihood of sticking increases as the printing speed increases. Conceivably, this is because the thermal paper sheet is pressed against the protective film 95 with a relatively large force and the resin coating is quickly heated and cooled in the high-speed printing.
Patent Document 1: JP-A-2002-2005